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Author Topic: Slow cranking CB750  (Read 1955 times)

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Offline zabzob

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Slow cranking CB750
« on: June 04, 2011, 11:52:16 AM »
My 1975 CB750K is cranking pretty slow (not starting) on what should be a fully charged battery. Just had it on the trickle charger a couple of days ago. Reads 12.5v engine off, 13.5-13.6v at 3000rpm. I can kick start it.

What else can cause this? Something wrong with the oil? It might have a bit of gas in it due to leaky carbs. I'm changing it tomorrow in any case.
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Offline Greggo

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Re: Slow cranking CB750
« Reply #1 on: June 04, 2011, 12:02:59 PM »
How many miles on the bike?  Starters do go bad..
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Offline zabzob

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Re: Slow cranking CB750
« Reply #2 on: June 05, 2011, 12:15:25 AM »
Greggo: I've got 28,500 miles on the bike. From Googling, it sounds like it could be a bad starter in need of a rebuild or replacement. Kits are on eBay for about $25 and shipping. I'll make sure it's nothing else before getting into this.

rotortiller: I'm unable to check the specific gravity as it's an AGM battery. New this year, and charged up on a fancy Honda branded Optimate 3+ trickle charger. It's got so many lights on it that it CAN'T be lying to me about the full charge.

I was under the impression that 12.5-12.6V was normal for a resting battery. I think I should have tested for the charging voltage at 4000rpm as per the FAQ, looking for about 14V. I'll do that tomorrow, along with the other tests recommended there.
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Offline phil71

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Re: Slow cranking CB750
« Reply #3 on: June 05, 2011, 11:29:37 AM »
does it start with the kicker?
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Offline zabzob

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Re: Slow cranking CB750
« Reply #4 on: June 05, 2011, 11:38:03 AM »
Yes, I can kickstart it. That's a little rough when it's cold, probably because the carbs aren't properly synced.
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Offline phil71

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Re: Slow cranking CB750
« Reply #5 on: June 05, 2011, 12:03:20 PM »
have you checked the contacts at the starter to see if they're loose, or dirty? Put on a glove and use an open end wrench to jump the starter solenoids 2 main connections, does the starter still spin slow?
 
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Offline zabzob

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Re: Slow cranking CB750
« Reply #6 on: June 05, 2011, 08:40:16 PM »
Well, I went out for a 50 mile ride today. Lots of riding right in the charging range. Highway stuff. Got very close to home, then it seems like it wants to die. Pulled up in front of my place, and while backing the bike in with the clutch in, it dies. Put the multimeter on the battery and it reads 5.5V. Took it inside and took another reading. 6V this time, slowly creeping up. 7v, 7.5V... now it's on the charger.

Probably a charging issue I guess.
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